抄録
This paper describes UV adhesive bonding of lithium niobate (LN) and silicon (Si), and the following polishing of LN, which are key technologies in wafer-level integration processes for LN acoustic devices on LSI. Five UV adhesive candidates were investigated in terms of bonding-induced stress and removability by O2 plasma treatment. The latter is important because the UV polymer is used as a sacrificial layer in the above processes. Based on the results, we selected one usable UV adhesive, and obtained bending-free LN/Si hybrid substrates, overcoming a large difference in the coefficient of thermal expansion between LN (7.5 (c-axis) - 14.4 (a-axis) × 10-6 /K) and Si (2.6 × 10-6 /K). The LN substrate on the Si substrate was thinned and surface-polished by an experimentally obtained recipe. Finally, a mirror-finished LN layer with a thickness of ca. 10 μm was successfully obtained without noticeable cracks. It was confirmed that this thin LN layer survived in the fabrication process of surface acoustic wave (SAW) devices.
